The polyphenolic pool of the heartwood of the mopane, Colophospermum mopane Kirk ex J. Leonard, exhibits extreme diversity and complexity. It comprises a variety of monomeric
flavonoids, e.g. flavan-3-ols, flavan-3,4-diols including the mopanols and peltogynols,
flavonols, dimeric
proanthocyanidins, e.g. proguibourtinidins, profisetinidins, promopanidins, propeltogynidins, and a variety of profisetinidin-type triflavanoids. The di- and tri-meric
proanthocyanidins are accompanied by several functionalized tetrahydropyrano- and hexahydrodipyrano-
chromenes (phlobatannins) that originate from the bi- and tri-flavanoids, respectively, via rearrangement of the
pyran heterocycle(s). Owing to the predominance of the 5-deoxy (A-ring) flavan-3-ols, the chain terminating moieties in the biosynthesis of oligo- and poly-meric
proanthocyanidins, the di- and tri-meric analogs also exhibit diversity as far as interflavanyl bonding positions are concerned. Such heterogeneity results from the reduced nucleophilicity of the A-rings of 5-deoxy flavan-3-ols, compared to the A-rings of the 5-oxy analogs (catechins), hence permitting alternative centers to participate in
proanthocyanidin formation. Biomimetic-type syntheses were extensively utilized to unequivocally establish constitution and absolute stereochemistry of both the conventional and
pyran ring rearranged-type di- and tri-meric compounds. Comprehension of the intricate mechanistic and stereochemical course of the
pyran ring rearrangement reactions also contributed significantly to unambiguous structure elucidations. The aerial parts of the mopane are rich in
essential oils that comprise mainly
alpha-pinene and
limonene, which are presumably responsible for the strong
turpentine odor of the pods. The leaves also contain significant concentrations of
beta-sitosterol and
stigmasterol which are apparently the source of
sterols in various organs of the mopane moth, Gonimbrasia belina. Three
diterpenes, dihydrogrindelic
acid, labd-13E-en-15-oate and
dihydrogrindelaldehyde are present in the bark and seeds, the latter compound exhibiting significant cytotoxicity against a human
breast cancer cell line.